Low-Frequency Noise Characteristics for Various -Added -Based 28-nm High- k/Metal-Gate nMOSFETs

In this letter, the effect of adding ZrO 2 to different positions in an HfO 2 -based high- k (HK) gate-stack is investigated by a low-frequency (1/f) noise measurement. The tested nMOSFETs are fabricated using 28-nm gate-last HK/metal-gate technology with a ~ 1-nm SiO 2 interfacial layer. The 1/ f noise mechanism of these devices is described by the carrier number fluctuation, and the extracted trap densities ( Nt )are 8.9 × 10 18 -5.1 × 10 19 eV -1 cm -3 . However, reference devices with a pure ZrO 2 gate dielectric exhibit 1/ f noise characteristics that are consistent with the unified model, which incorporates both the carrier number and the correlated mobility fluctuations. The reference devices are with lower Nt values in the range of 5.8 × 10 17 -2.4 × 10 18 eV -1 cm -3 . In addition, there is an increase in Nt as the initial HfO 2 layer becomes thicker.These results show that the trapping behavior is mainly dominated by the HfO2 film and is dependent on the thickness of the initial HfO 2 layer in the ZrO 2 /HfO 2 /SiO 2 gate-stack.